Why use milestone in the project?

Milestones is used to check on the health of your project. Milestones provide an opportunity to validate the current state of the project.

A milestone is a scheduling event that signifies the completion of a major deliverable or a set of related deliverables. A milestone, by definition, has zero duration and no effort. A milestone is a marker in your schedule. You don't place milestones in your schedule based on a calendar event. In other words, you don't schedule a milestone for the first Friday of every month.

Quote from Tech Republic:

Milestones are great for managers and the sponsor because they provide an opportunity to validate the current state of the project against the overall schedule. Since each milestone signifies that some set of underlying work has been completed, your sponsor should know immediately that your project is behind schedule if a milestone date is missed. The sponsor does not need to know the individual status of all the activities in the workplan. He just needs to keep track of the status of the milestones to know if a project is on schedule or not.

In addition to signifying the status of the project against the workplan, milestones also provide a great way to take a step back and validate the overall health of the project. In particular, the following types of activities can be scheduled for (or at) each major milestone.

* Validate that work done up to this point is complete and correct.
* Make sure that the sponsor has approved any external deliverables produced up to this point.
* Check the workplan to make sure that you understand the activities required to complete the remainder of the project. You did this when the project started, but each milestone gives you a chance to re-validate that you still understand what is required to complete the project.
* Double-check the effort, duration, and cost estimates for the remaining work. Based on prior work completed to date, you may have a much better feel for whether the remaining estimates are accurate. If they aren't, you'll need to modify the workplan. If it appears that your budget or deadline will not be met, raise an issue and resolve the problems now.
* Issue a formal status update and make any other communications specified in the Communication Plan.
* Evaluate the Risk Management Plan for previously identified risks to ensure the risks are being managed successfully. You should also perform another risk assessment to identify new risks.
* Update all other project management logs and reports.

These activities should be done on a regular basis, but a milestone date is a good time to catch up, validate where you are, get clear on what's next, and get prepared to charge ahead.